The present invention refers to a device for filling and closing disposable bags suitable for containing paper documents, in particular banknotes.
Such a device is intended to be used in machines for storing banknotes, normally present at banks, supermarkets, shopping centres or similar.
Devices of this type, characterised by a structure that comprises an upper container for temporarily housing one or more banknotes (provided with an opening on the bottom for the controlled exit of the banknotes) and a lower element with a plane for supporting the bag intended to be filled with the banknotes, placed below the opening in the bottom of the upper container, are described for example in Italian patent applications MI2013A000753 and MI2013A000751 to the same Applicant. The lower plane for supporting the bag containing the banknotes is vertically movable, against the action of compression or traction springs, so as to progressively lower as the number of banknotes that enter into the bag increases, due to the thickness of the banknotes.
In such devices, the controlled transfer of the banknotes from the upper container to the bag supported on the lower movable plane takes place thanks to the thrust of a vertically movable piston inside the upper container to push the banknotes downwards so as to force them to pass through the opening on the bottom of the container. Once the passage has occurred, and the banknotes have been introduced into the bag, the thrust of the piston contributes to lowering the lower movable plane.
Once the bag is filled, it is closed by means of a pair of sealing bars arranged between the bottom of the upper container and the lower movable plane, after having retracted the piston taking it back into its upper position so as not to interfere with the blades themselves.
Following the retraction of the piston, however, the force of the compression or traction springs (now only counteracted by the weight of the banknotes, but no longer by the thrust of the piston) causes the lower movable plane to lift until the banknotes rest (with the bag interposed) against the lower surface of plates or other appropriate protective elements of the sealing bars, which are usually provided to avoid direct contact between the bag and the bar moving mechanisms. In this situation, with the banknotes pressed (with interposition of the bag) against the aforementioned protective elements, the actuation of the sealing bars causes traction of the bag, making it move in the area adjacent to the bars themselves.
This movement of the bag causes a movement of the banknotes present in the upper portion of the stack, which are in contact with the bag itself and immediately adjacent thereto.
Depending on the friction coefficient of the bag (thus based on the physical and mechanical properties of the bag), the behaviour of the banknotes can be different. For example, if the bags have a low friction coefficient and are not very rigid, the displacement of the banknotes due to the movement of the sealing bars can be minimal and thus negligible.
On the contrary, in the case of bags with a high friction coefficient, or with a greater degree of rigidity, the movement of the sealing bars can produce a significant displacement of the banknotes, which tend to move as a whole with the bars themselves. In this case, the banknotes can become pressed between the bars or, in the worst case, even come out from the bag. It is clear that in these cases a correct sealing of the bag cannot be obtained because a banknote is interposed between the bars, thus preventing the two edges of the bag from being joined.
In order to avoid this problem, the action of the springs pushing the lower movable plane for supporting the bag must be annulled during the sealing process and, at the same time, the banknotes must be kept spaced from the protective plates of the sealing bars, so that the bars can advance without the banknotes moving together with the bag, which, on the other hand, is free to move together with the bars.
In the prior art, solutions to prevent the movement of the lower movable plane can provide for the use of electric motors, clutches, solenoids, etc. All of these solutions, however, involve remarkable mechanical or electronic complexity. For example, the application and use of an electric motor or of a clutch require a lot of space and their management can prove complex and difficult, both for effective control of the actuation steps, and to obtain adequate precision in the positioning of the support plane.
The use of a solenoid, on the other hand, can cause problems connected with the reliability of maintaining the support plane in locked position, which is continuously strained by the action of the pushing spring.